1. Field of the Invention
The present invention relates to a heat pump water heater outdoor unit and more specifically to a heat pump water heater outdoor unit in which a refrigerant is injected during a compressing process to improve an ability to supply high-temperature water and a heating ability at a low ambient temperature, and a heat pump water heater equipped with the heat pump water heater outdoor unit.
2. Description of the Related Art
A heat pump utilizing heat energy in air has been used for a water heater or an air conditioner as an energy-saving heat source. In the case of running the heat pump water heater or air conditioner in a high-temperature (for example, 60° C.) water supply mode or a quick heating mode at low temperatures (for example, −15° C.), an evaporation temperature of an evaporator decreases. Therefore, if a refrigerant is compressed to a predetermined pressure, a temperature of the refrigerant discharged from a compressor increases. At this time, an overtemperature protection function for a discharge refrigerant temperature is performed to ensure a reliability of the compressor, to thereby decrease a capacity (number of revolution) of the compressor. This causes a problem of decreasing an operating ability (a heating/hot water supply ability of the water heater or a heating ability of the air conditioner).
To solve the above problem, as a mechanism for injecting a refrigerant during a compressing process of a compressor, for example, the following air conditioner is proposed (for example, in Japanese Unexamined Patent Application Publication No. 2006-112753). The air conditioner is constituted such that it comprises an outdoor unit 1 incorporates a compressor 3, a four-way valve 4 for switching between a heating mode and a cooling mode, an outdoor heat exchanger 12, a first expansion valve 11 as a first decompression device, a second internal heat exchanger 10, a third expansion valve 8 as a third decompression device, an injection circuit 13, a second expansion valve 14 as a second decompression device, an intermediate-pressure receiver 9, and a refrigerant heating heat source 17; a suction pipe 18 of the compressor 3 passes through the intermediate-pressure receiver 9, so that a refrigerant in a through pipe 18a of the suction pipe 18 and a heat exchange refrigerant 9a in the intermediate-pressure receiver 9 can exchange heat; and in addition, the refrigerant heating heat source 17 heats a refrigerant flowing through the injection circuit.
Further, for example, the following air conditioner is proposed (for example, in Japanese Unexamined Patent Application Publication No. 2006-258343). The air conditioner includes a main refrigerant circuit 20 (hereinafter also referred to as “main refrigerant pipe”) constituted by connecting an injection-port-equipped compressor 1, a four-way valve 2, an indoor heat exchanger 3, a first expansion value 4, an supercooling heat exchanger 5, a second expansion valve 6, and an outdoor heat exchanger 7 in sequence, and a first bypassing circuit 21 constituting an injection circuit extending from a point between the second expansion value 6 and the supercooling heat exchanger 5 to an injection port of the compressor 1 through a third expansion value 8, the supercooling heat exchanger 5, a refrigerant heating unit 9 and a first opening/closing valve 10″.
Further, for example, the following heat pump water heater is proposed (for example, in Japanese Unexamined Patent Application Publication No. 2007-132628). The water heater is mainly composed of a hot water storage circuit 1K including a hot water cylinder, a circulation pump, and a heating heat exchanger, which are connected into circularly with hot water piping, a hot water supply circuit 2K for supplying hot water in the hot water cylinder to a target portion, a refrigerant circuit R including a compressor capable of adjusting a compression power in two stages, the heating heat exchanger, a cooling device, a first electric expansion valve, and an evaporator, which are connected circularly with refrigerant piping, and an intermediate injection circuit M that branches off from the refrigerant circuit at a point between the heating heat exchanger and the cooling device, and is provided with an electromagnetic opening/closing valve, a second electric expansion valve, and the cooling device and configured to cause a part of the refrigerant discharged from the heating heat exchanger to flow back to a portion between a low-pressure side and a high-pressure side of the compressor”.
However, Japanese Unexamined Patent Application Publication Nos. 2006-112753 and 2006-258343 that disclose the air conditioner equipped with the injection circuit describe only advantages or control processes applicable for the air conditioner equipped with the injection circuit, but not describe advantages or control processes for a heat pump water heater equipped with a water heat exchanger. Thus, the disclosed air conditioner cannot be easily applied to a heat pump water heater with a higher load and larger load change than the air conditioner.
Further, a conventional heat pump water heater (for example, see Japanese Unexamined Patent Application Publication No. 2007-132628) has no function of stabilizing a refrigerant condition in a water heat exchanger (condenser in a heating/hot water supply mode), which varies along with a load change of the water heat exchanger, and has a problem of an unstable heat exchange performance of the water heat exchanger.